1. Field of Invention
The present invention relates to hydrogen absorbing tank apparatus.
2. Description of Related Art
In a conventional art, when hydrogen gas that is stored by absorption or occlusion in a hydrogen absorbing tank is to be extracted from the tank and supplied to a fuel cell, the hydrogen absorbing tank needs to be heated by using hot water or the like in order to provide release heat for releasing hydrogen gas from a hydrogen absorbing material. For example, in a system where hydrogen gas is extracted from a hydrogen absorbing tank and supplied to a fuel cell, heat produced by the fuel cell is used to heat a hydrogen absorbing material disposed in the hydrogen absorbing tank.
Furthermore, in order to ensure that the hydrogen gas producing pressure at which hydrogen gas is released from the hydrogen absorbing tank will be equal to or higher than a reference pressure of a hydrogen gas consumer device (e.g., the fuel cell), the hydrogen absorbing tank needs to be heated to a predetermined temperature when it is at a relatively low temperature or the like.
In a fuel cell used as a source of drive energy for a vehicle, it is important to quickly supply hydrogen gas to the fuel cell to promptly cause the fuel cell to start generating power. However, if the hydrogen absorbing tank for supplying hydrogen gas to the fuel cell has a low temperature, for example, when the vehicle ambient temperature is low, the hydrogen producing pressure becomes low and the amount of hydrogen gas supplied to the fuel cell is low. In such a case, there is a danger of insufficient power generation, and also a danger of insufficient heat supply from the fuel cell to the hydrogen absorbing tank, which will result in a further delay of the start of power generation of the fuel cell. A delay of the start of power generation at the time of hydrogen release from the hydrogen absorbing tank also occurs when hydrogen gas is supplied from the hydrogen absorbing tank to a hydrogen gas consumer device other than a fuel cell for generating vehicle driving energy.
A conceivable measure for improving the aforementioned situation at a low temperature is to employ a hydrogen absorbing material whose hydrogen producing pressure is high at low temperatures. However, if this measure is adopted, the hydrogen producing pressure becomes too high after the fuel cell is started up or when the ambient temperature is high. Therefore, this measure requires an increase of the pressure resistance of the hydrogen absorbing tank and limits the variety of hydrogen absorbing materials that can be used.
Japanese Patent Application Laid-Open No. HEI 7-37598 proposes that a heating wire be added to a hydrogen absorbing tank so that the hydrogen absorbing tank can be heated by electrifying the electric heater (i.e., the heating wire).
However, the supplemental electrical heating of a hydrogen absorbing tank has significant problems in safety and electric energy consumption. Normally, the amount of heat generated by a heating wire is considerably less than that generated by a hydrogen gas consumer device such as a fuel cell or the like. Therefore, the supplemental electrical heating only slightly accelerates the heating of a fuel cell; that is, the heating rate is increased only slightly from the level achieved without the supplemental electrical heating.
As another conceivable measure, a burner capable of producing larger amounts of heat than an electric heater may be externally provided so that combustion gas from the burner is used to heat a hydrogen absorbing tank. However, this measure causes problems of fuel storage requirement, complication of the system, degradation of safety, deterioration of efficiency, and the like.